In semiconductor industry, it is common to use wafers to fabricate various types of electronic product devices such as integrated circuits (ICs), solar cells and light-emitting diodes (LEDs). A wafer is a thin slice of semiconductor material. Microelectronic devices are built in or over the wafer by applying micro-fabrication processes such as doping, ion implantation, etching, deposition and photolithography. Then, the circuits on the wafer are separated by a process called dicing and packaged.
Particularly, an epitaxial wafer is a high quality wafer made by an epitaxial growth process. During the epitaxial growth process, one or more crystalline overlayers (referred to as epitaxial layers) are deposited on a crystalline substrate. The crystalline substrate serves as a seed crystal. The crystalline overlayer forms an ordered crystal orientation with respect to the crystal structure of the crystalline substrate. The epitaxial layers and the substrate can have the same material (homoepitaxy) or different material (heteroepitaxy).